Lithography is common for use in digital label press and packaging printing. In the offset process, the image may be indirectly applied to the media, such as paper or other materials, through an intermediate transfer, or blanket cylinder, whereby the image from the plate is applied first to a blanket cylinder, which then offsets, or transfers, from the blanket cylinder to the media. Typical lithographic and offset printing techniques utilize plates that are permanently patterned, and are, therefore, useful only when printing a large number of copies of the same image, such as magazines, newspapers, and the like.
Digital offset lithographic printing has been developed as a system that uses a non-patterned re-imageable surface, which is initially uniformly coated with a dampening fluid layer. Regions of the dampening fluid are removed by exposure to a focused radiation source (e.g., a laser light source) to form pockets. A temporary pattern in the dampening fluid is thereby formed over the non-patterned re-imageable surface. The digital offset-type ink applied thereover is retained in the pockets formed by the removal of the dampening fluid. The inked surface is then brought into contact with a substrate, such as paper, plastic or metal and the ink transfers from the pockets in the dampening fluid layer to the substrate. The dampening fluid may then be removed, a new uniform layer of dampening fluid applied to the re-imageable surface, and the process repeated. For example, an inker subsystem may be used to apply a uniform layer of digital offset-type ink over the layer of dampening fluid. The inker subsystem may use an anilox roller to meter the ink onto one or more ink forming rollers that are in contact with the re-imageable surface.
Digital offset lithographic printing systems use offset-type inks that are specifically designed and optimized to be compatible with the materials the ink is in contact with, including the re-imageable surface and the dampening solution as well as with the various subsystems used during the printing process to enable high quality digital printing at high speed.
Digital offset printing inks differ from conventional inks because they must meet demanding rheological requirements imposed by the lithographic printing process while being compatible with system component materials and meeting the functional requirements of sub-system components, including wetting and transfer. Print process studies have demonstrated that higher viscosity is preferred for ink transfer to digital lithography imaging blanket from the inker unit via a roll and yet even higher viscosity is needed to improve transfer to a print substrate.
Accordingly, digital offset inks require a specific range of viscosity, tack and tack stability to afford sufficient and predictable ink cohesion to enable good transfer properties in and among the various subsystems.
Currently, only few examples of digital offset-type ink are commercially available. These examples include UV curable inkjet types and hot-melt adhesive dispensers, such as, those from Nordson or Marco.
Therefore, there remains a need for digital advanced lithography imaging inks to have increased viscosity latitude to enable excellent ink transfer from the ink loader system at both about 60° C. and excellent ink delivery from the anilox roller to the fluorosilicone blanket at temperatures as low as about 20° C.